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My lab is a broadly based plant ecology lab—with research
ranging from reproductive biology to physiology to community ecology
and with a tradition of encouraging independent exploration in
new research directions. Students are free to participate in my
research if they choose but often pursue unrelated projects guided
by their own interests.
Arbuscular mycorrhizal communities
With the goal
of understanding how soil types and host plant species influence
the community structure of AM fungi, we have compared
the AM fungal communities
on the same host plant species (all C4 grasses) but in two very different soils—in
tall grass prairie remnants at two sites in Iowa and in Eastern serpentine grasslands.
Serpentine soils have elevated levels of Mg, relative to Ca, and other potentially
toxic heavy metals (Cr, Ni) but are deficient in some important nutrients. In
these systems, the taxonomic structure of AM fungal communities seems to be influenced
much more by soil characteristics than by the identity of the host plant species.
Further evidence of ecological matching between AM fungal communities and their
soils comes from a greenhouse experiment in which we switched the fungal communities
between the prairie and serpentine systems and found that plants grew better
with native fungi. When the same AM fungal community is added to plants in the
two different soils, the composition of the communities also diverges. These
results suggest that some fungal species are better suited for serpentine while
others are better suited for prairie soils and soil traits shape AM fungal communities.
We also find evidence of functional variation within a single population of the
fungal species Gigaspora gigantea. This is exciting as it suggests that some
of the feedback we have detected between plants and their AM fungi may be due
to intraspecific fungal variation.
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Spores of the arbuscular mycorrhizal
fungus Gigaspora gigantea |
We are also exploring functional differences
among co-occurring AM fungi with the idea of explaining why a single host plant
normally harbors more than one
fungal species. Previous studies have evaluated the benefit AM fungi provide
to the host by comparing plant growth in response to a single AM species with
plant growth when no fungi are present. Our unique approach to understanding
the functions of different fungal species involves infecting the plant with
several species simultaneously and then evaluating the effect on
host plant growth when
one of the species is omitted from the community. By repeating the experiment
under different soil conditions we can determine whether the benefit provided
by a particular AM species depends on soil composition. If so, this would be
an example of niche partitioning among the fungi. Anatomy and demography of
an herbaceous desert perennial
Desert annuals are well
studied but little is known about the growth responses of herbaceous
perennials to the variable precipitation
that characterizes desert
systems. We draw from long-term demographic studies and studies of root anatomy
and vascular architecture to understand the response of Cryptantha flava (Boraginaceae) to extended drought and large precipitation pulses.
Recent experiments demonstrate
that individual lateral roots supply water to a different portion of the
shoot. Plants may shrink due to the death of these plant segments.
We are also interested
in whether shrinkage is an expression of senescence in this species.
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Cryptantha flava,
the species used in demographic and physiological studies
of drought consequences. |
Plant
ecology research in northern Mongolia
Starting in Summer 2008, the
Casper lab will be participating in a five-year, NSF-funded research
project in northern Mongolia
to examine the ecosystem
consequences of rising temperatures and increased grazing pressure
from domestic herds.
That part of the world is expected to experience some of the greatest
temperature increases as a consequence of global warming.
The particular study site
was selected
because steppe grasslands and larch forests, two important world biomes,
converge there, and the larch forest appears not to be regenerating.
The Casper lab
will focus on changes to the plant community. Soil factors are also
of interest, but
the remoteness of the site will limit the types of soil factors that
can be measured.
Research history
Initially, my own interests (and graduate training)
were in the area of pollination biology and plant breeding systems,
which led me to studies
related to the
evolution of fixed embryo abortion and distyly, as a breeding system.
I
have also examined
how soil nutrient heterogeneity changes rooting distributions of
competing plants and investigated the consequences of soil
heterogeneity for
the size structure
of plant populations. Thus, I feel comfortable supervising graduate
research conducting research in diverse areas of plant
ecology.
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People